Vulcanization of fluoroelastomers

ABSTRACT

Process for vulcanizing fluoroelastomers by heating the elastomer in the presence of a secondary monoamine and an aromatic polyamine or aromatic polyol. Vulcanizates with outstanding physical properties are obtained from this reasonably rapid, low-scorch curing process.

United States Patent Inventor William John Keller Wilmington, Del.

Appl. No. 853,529

Filed Aug. 27, 1969 Patented Nov. 23, 1971 Assignee E. I. du Pont deNemours and Company Wilmington, Del.

Continuation-impart of application Ser. No. 536,641, Mar. 23, 1966, nowabandoned. This application Aug. 27, 1969, Ser. No. 853,529

VULCANIZATION OF FLUOROELASTOMERS 1 1 Claims, No Drawings 260/85.5 S,260/87.7 Int. CL C08f 27/08 Field of Search 260/80.77,

Primary Examiner-Joseph L. Schofer Assistant Examiner-Stanford M. LevinAuomey-Vemon R. Rice ABSTRACT: Process for vulcanizing fluoroelastomersby heating the elastomer in the presence of a secondary monoamine and anaromatic polyamine or aromatic polyol. Vulcanizates with outstandingphysical properties are obtained from this reasonably rapid, low-scorchcuring process.

VULCANIZATION OF FLUOROELASTOMERS This application is acontinuation-in-part of applicant's copending application, Ser. No.536,641, now abandoned.

BACKGROUND OF THE INVENTION vulcanization of fluorine-containingpolymers is often accomplished by using carbamates of aliphatic diaminessuch as ethylene diamine carbamate or the more generally preferredhexamethylene diamine carbamate as is disclosed in US. Pat. No.2,979,490 to West. Unfortunately, during the processing offluoroelastomer compositions, the carbamates of aliphatic diamines canpromote scorching or premature vulcanization, which produces difficultyin processing and molding of the compositions into finished articles.Various attempts have been made to overcome the problem of scorching,but additional problems have thereby been introduced because thevulcanization systems which are satisfactory for scorch resistance arenot entirely satisfactory in producing a highly developed cure in thefluoroelastomer, especially a cure with good resistance to compressionset.

Curing fluoroelastomers with aromatic polyamines has been considered,but there are serious problems associated with their use, most importantof which are (1) an extremely slow rate of reaction between the aromaticpolyamines and the fluoroelastomers, (2) a poorly developed cure aftervulcanization, particularly with regard to resistance to compressionset, and (3) the need for high concentrations of the polyamines toachieve even a mediocre result.

U.S. Pat. No. 3,041,316 to Grifiin discloses the room temperature cureof fluoroelastomers with a monoamine-aliphatic diamine ormonoamine-aliphatic mercaptan system. While such systems are somewhateffective for special applications in which the elastomer is cured atroom temperature, they are too scorchy for thermal cures at thetemperatures necessary to process and shape fluoroelastomer stocks.

SUMMARY OF THE INVENTION This invention provides a process forvulcanizing a fluoroelastomer by mixing said elastomer with (l) adialkyl, dicycloalkyl, or alkylene secondary monoamine of not more than24 carbon atoms in an amount which provides about 0.020.4 part of aminonitrogen per 100 parts of fluoroelastomer and (2) about 0.5-2 parts byweight per 100 parts of fluoroelastomer of a polyfunctional aromaticcompound having no more than 3 aromatic rings and having at least 2hydroxyl or primary amino groups attached to an aromatic nucleus, andheating the mixture to about 100250 C.

DETAILED DESCRIPTION The curing process of this invention is applicableto any vulcanizable fluoroelastomer. By fluoroelastomer" is meant acopolymer of vinylidene fluoride and at least one other ethylenicallyunsaturated fluorinated monomer. Such monomers ordinarily contain from 2to 6 carbon atoms. Representative of such monomers arehexafluoropropene, tetrafluoroethylene, l,2,3,3,3-pentafluoropropene, l,1 ,3,3,3- pentafluoropropene, chlorotrifluoroethylene, perfluoroacrylicacid and its derivatives, such as the acid fluoride andperfluoroacrylonitrile. The copolymers usually contain at least about 30percent by weight vinylidene fluoride.

Preferred copolymers are those derived from vinylidene fluoride andhexafluoropropene wherein the vinylidene fluoride is about 70 to 30percent by weight and the hexafluoropropene is about 30 to 70 percent byweight. Other preferred copolymers are vinylidenefluoride/hexafluoropropene/tetrafluoroethylene terpolymers andcopolymers of vinylidene fluoride and 1,2,3,3,3-pentafluoropropene orl,l,3,3,3-pentafluoropropene. Further information regarding suitablecopolymers and processes for their preparation can be found in US. Pat.Nos. 3,051,677 to Rexford and 2,968,649 to Pailthorp and Schroeder.

The secondary monoamines, which are a part of the vulcanization systemsfor the fluoroelastomers, are the dialkyl and dicycloalkyl secondarymonoamines and the alkylene secondary monoamines each of which shouldhave not more than about 24 carbon atoms. By alkylene secondarymonoamines is meant those having both terminal carbons of the alkylenegroup attached to the NI-I group as in piperidine. Representativedialkyl secondary monoamines are diethyl amine, dibutyl amine, anddidodecyl amine. A representative dicycloalkyl secondary monoamine isdicyclohexylamine. The amounts of secondary monoamine which are usefulare described best in terms of their nitrogen content, and they lie inthe range of 0.02 to 0.4 parts of amino nitrogen per parts by weight ofthe copolymer. Higher or lower amounts of the monoamines can be used.However, higher amounts increase the cost unduly and the state ofvulcanization achieved by smaller quantities is undesirably low. Thepreferred amounts of secondary monoamine are those which provide about0.1-0.2 part of amino nitrogen to the vulcanizing system. Since some ofthe secondary monoamines are volatile, e.g., diethyl amine, it issometimes more practical to use them in the form of their salts, such astheir carbamates or acetates, and the term secondary monoamine" as usedherein should be construed to include such salts.

The aromatic polyfunctional compounds which are part of thevulcanization system are those containing not more than 3 aromaticrings, wherein there are at least 2 hydroxyl or primary amino groupsdirectly attached to an aromatic nucleus. Representative compounds aremetaand para-phenylene diamine, hydroquinone, 2,6-diaminotoluene,2,4-di(paminobenzyl)aniline, p-aminophenol, l ,2,4-triaminobenzene, andmethylene dianiline. Preferred compounds are p-phenylene diamine andhydroquinone because of their reasonable reaction rates and theoutstanding vulcanizate properties they give. The amounts of thepolyfunctional aromatic compounds needed for economical and rapidvulcanization are in the range of about 0.5-2 percent by weight of thecopolymer. The preferred amounts are about 0.75-] .5 percent based onthe copolymer.

The method of using the curing systems of this invention is toincorporate the components into a typical fluoroelastomer optionallycontaining conventional compounding agents such as a metal oxide and areinforcing filler such as carbon black. The preferred method ofincorporation is by milling on a 2-roll rubber mill, but other mixingequipment can be used. It is also practical to make solvent solutions ofthe copolymer and to incorporate the vulcanizing agents by stirring theminto the solution. Regardless of the method used, the ingredients of themixture can be incorporated separately, i.e., as the free monoamine andpolyamine or their salts, or as complex compounds of the monoamine andpolyol, or as mixed amine carbonates such as those shown in theexamples. The monoamine and polyfunctional agents can be addedsimultaneously or consecutively.

After incorporating the vulcanizing system into the copolymer,vulcanization is effected by heating the composition at about l00-250 C.Typically a two-step process is employed. In the first step, thecompounded elastomer is cured in a press and compression mold to fonnthe composition into desired products for use or for testing. Theheating in this step is usually done at l50-200 C. for 30 to 60 minutes.In the second step, the shaped piece is removed from the mold and thepress and heating is continued at atmospheric pressure in an air ovenfor 18 to 24 hours at 200-250 C. until a high state of vulcanization isreached.

The invention is illustrated by the following examples wherein parts andpercentages are by weight unless otherwise specified.

EXAMPLE 1 Procedure for Compounding and Vulcanizing Copolymers On acool, 2-roll rubber mill, 100 parts of a copolymer of about 60 percentvinylidene fluoride and about 40 percent hexafluoropropene is compoundedwith 20 parts of medium thermal carbon black and parts of magnesiumoxide. Except as noted, 135 parts of this composition is used forfurther compounding with the vulcanizing agents described in theexamples. After completion of the compounding, the compositions aresheeted off the mill and specimens for physical testing are prepared bycompression molding in a press for 30 minutes at 190 C. followed byremoving them from the mold, and postcuring" by heating in an air ovento 204 C. over a 4- hour period and then an additional 24 hours at thistemperature.

p-Phenylene Diamine and Diethyl Amine p-Phenylene diamine and diethylamine are used as the vulcanizing agents in the proportions shown intable l. Care must be used to avoid prolonged milling and excessivetemperature during milling, which conditions promote excessivevolatilization of the amine. Typical results of physical tests on thevulcanizates are shown in table I.

The procedure of example 1 is followed using 2.9 parts of the abovecompound as the vulcanizing agent. The scorch test at l2l C., accordingto ASTM D-1646-6l, shows that the compounded stock has a minimum valueof 20 units and after minutes, the value is only 30 units.

p-Phenylene Diamine and a High Molecular Weight Secondary Amine Theprocedure of example 1 is followed with 1.1 parts of pphenylene diamineand 3.5 parts of di-n-dodecylamine used as the vulcanizing agents.

TABLE I 1 X A B C D Control Parts of p-phenyiene diamlno 1.0 1.0 0. 60.5 1 Parts of diethyl amine 0. 1 1. 0 1.0 2. 0 Physical propertiesmeasured (25 C.)

Aftge press vulcanization for 30 min. at

Modulus at 100% elongation, p.s.i 200 600 350 500 Tensile strength,p.s.i 750 1,700 1,575 1, 425 U) Elongation at break, percent". 750 265365 255 Permanent set at break, percent J5 10 15 8 After posteure at 2040.:

Modulus at 100% elongation, p.s.i 400 1, 450 320 1, 275 200 Tensilestrength, p.s.i. 2, 250 2, 400 1, 550 1,575 1, 280 Elongation at break,percent 220 135 160 125 510 Permanent set at break, percent 6 4 3 5 42Hardness, Durometer A 7 71 73 61 Compression set, 22 hrs. at 70 C s 11 a100 1 Control experiment outside the invention for comparison only. iInsufficient vulcanization.

If, for comparison, a mixture is made wherein 1 part of TABLE llldiethyl amine is used in the'absence of p-phenylene diamine, after the190 C. press vulcanization, there is not sufficient An" NW Cvulcanization to provide meaningful test data. After the 204vulcanization Pustcun: C. postcure, a tensile strength of 2,250 p.s.i.,and an elongation at break of 355 percent are obtained, but the specimenModulus! s um 1.100 for testing compression set resistance IS porous dueto insufi'i- $3 S!rr,-ng1h,p.$.i. 1.300 1,150 cient vulcanization, andmeaningful test data are not obtained. Elnnsminn m Break 1 395 noPermanent Set :1! Break. 2 I7 I Compression Sci. 22 hrs. at EXAMPLE 2 C"q 9 Hydroquinone and EXAMPLE 4 v Diethyl Amine p-Phenylene Diamine and aA compound of 2 moles of hydroqumone and 1 mole of Hemroc clic Aminediethyl amine is prepared by adding 6 parts of diethyl amine to y 4.4parts of hydroquinone dissolved in a vessel containing 53 A compound isfonned by saturating with CO at room temparts of ethyl ether, andcooling the mixture in an ice bath. A perature a solution made from 89parts of tetrahydrofuran and crystalline appearing solid appearsrapidly. After allowing the 6.5 parts of p-phenylene diamine, and thenintroducing 5 parts vessel and contents to stand overnight, the solidproduct is of piperidine. A crystalline-appearing solid is formed whichis recovered by filtration and dried at 40 C. in a vacuum oven. filteredand dried in air at 25 C. Analysis for C H N O, Analysis for C H O Nshows 65.7 percent carbon, 8.0 pershows 60.7 percent carbon, 8.0 percenthydrogen and H0 percent nitrogen.

cent hydrogen and 4.49 percent nitrogen The procedure of example 1 isfollowed using 1.8 parts of g :1 BreaB JZk at 1.0217) 2 l the abovecompound as the vulcamzmg agent. a m

TABLE IV 5 EXAMPLE 7 vulcanization of a Vinylidene Fluoride/ After 190C.

Press After 204 C. vulcaniwmn Pom":Hexafluoropropene/Ietrafluoroethylene Copolymer with Methylenedianilineand Diethyl Amine Modulus at 100% Elongation. p.s.i. 400 1.200 At about20 C. a solution of parts dlethyl amtne in 89 s:h. psi- L850 1950 partsof tetrahydrofuran is stirred in a closed glass vessel. An atmosphere ofCO is maintained in the vessel until CO ab- Permanent Set at Break. '2l0 4 Communion 22 hm sorpt1on stops. A solution of 39.6 parts ofmethylenedlamlme at 70 0,91 0 15 in 50 volumes of tetrahydrofuran isadded dropwise to the diethyl amine solution while simultaneouslymaintaining the atmosphere of CO When CO absorption stops, the reactionmass which is now a white slurry is filtered, and solvent is EXAMPLE 5removed under vacuum at room temperature. Melting point of Ph l h I thesolid product recovered is about 8285 C. any ene 'amme 1e! y Theprocedure of example 1 is followed using 2.4 parts of Amine-CO Compoundthe above compound as the vulcanizing agent. except the co l mer used isa vin lidene fluoride, tetrafluoroeth lene,

A ompound of piphenylene methyl amme and he flitoropropene cop olymer,containing the folliiwing -CO,1s prepared by d1ssolv1ng, at roomtemperature, 54 parts respective mole percentages: 36 39 and 25 and thepress of the p-phenylene diamine in 119 parts of methanol concureis 40min at 200C tained in a 2-neck glass flask, equipped for stirring andsaturating the solution with CO To the saturated solution, main- TABLEV" tained under a C0 atmosphere, 36.5 parts of diethyl amine isintroduced dropwise with stirring during 3 hours. The solvent is thenremoved under vacuum and a finely divided brown Ph s1cal Pro ertiesObtained powder is recovered. This is passed through a -mesh screen y Pbefore use. Analysis for C I-1, 0 1% shows 59.6 percent car- FromPostcured Specimens bon, 7.8 percent hydrogen and 17.6 percent nitrogen.

The procedure of example 1 is followed using 2.2 parts of 35 -rc. 100C.the above compound as the vulcanizing agent. The scorch test at 121 C.according to ASTM D-l646-6l shows that the Mod 1 100% El 1 94 ascompounded stock has a minimum value of 24 umts and after z fz i n p 8,3 min. running, the value is 45 units. 121011 1111011 111 Break. a 2110250 The following physical properties are obtained at 25 C.: 40 Q 9Hardness. Dummcter A 84 Compression Set. 22 hrs. at 70 C. 25 TABLE vCompression Set. 70 hrs. at l2lC. 28

After 190 C Press After 204C. 4 EXAMPLE 8 A compound is formed bysaturating with CO, at room temperature a solution made from 133 partsof tetrahydrofuran rr 700 and 8 parts of p-phenylenediamine and thenintroducing 13.2 Sums! PM 50 parts of dicyclohexylamine whilemaintaining the C0, at- 151011 1111011 at Break. a 170 so mosphere. ASolid forms rapidly and 1s recovered by flltrauon. t at Brwk- Q 4 4 Thissolid (20 parts) is treated at room temperature in a ggfg' 42 a Rotovacto remove residual solvent. Analysis for C H N Dummm, A 74 0, shows 691percent carbon; 9.7 percent hydrogen; and l0.8

percent nitrogen.

The procedure of example 1 is followed using 2.5 parts of EXAMPLE 6 theabove compound as the vulcanizing agent.

Vulcanization of a Vinylidene Fluoride/ T ABLE vml,2.3.3.3-Pentafluoropropene Copolymer The procedure of example 1 isfollowed except the copolymer used is a copolymer containing 77 molepercent of PHYSICAL PROPERTIES MEASURED C) Vinylidene fluoride and 23mole Percent of 1 9 After Press vulcanization for 30 Minutes at 190C.tafluoropropene. The vulcanizing agent is the compound of example 5 and1.5 parts are used. The following physical propenies are obmined at 50MOdtlILIS at I00; Elongation-psi 300 Tensile Strength-ps1. 1.650Elongation at Break-'71 310 TABLE VI Permanent Set at Break-'1' 10 AfterPostcure at 204 C.

After 190* C. Press After 204 C. vukuninuiu" pmcmc Modulus at 100 2Elongation-psi. 800 Tensile Strength-psi. 2.250 I Elongation at Break-ZI90 Modulus at I00; Elongation. permanent 5 m 5 q 6 psi 200 L000 75Compression Set. 22 hrs. at C. 1 l4 Tensile Strength. p.s.i. 300 2.300

IOI RBOI 0499 Thecopolymer compositions containing the vulcanizationsystems of this invention are superior to compositions based oncarbamates of aliphatic diamines, because they combine safety frompremature vulcanization (scorch) during processing with excellentelastomeric properties after the twostep vulcanization process. In manyof the compositions a high level of elastomeric properties is attainedafter the first step of the vulcanization process indicating the unusualefficiency of the novel systems. All this is achieved with lowconcentrations of the curing system.

As many widely different embodiments of this invention may be madewithout departing from the spirit and scope thereof, it isto beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims, and allchanges which come within the meaning and range of equivalence areintended to be embraced therein.

EXAMPLE 9 For comparison purposes, the copolymer of example 1 isvulcanized with two curing systems of this invention and several of theprior art.

Six samples (A-F) of the compounded vinylidenefluoride/hexafluoropropene copolymer are prepared by milling 100 partsof the copolymer, 20 parts of medium thermal carbon black and 15 partsof magnesium oxide on a cool, 2-roll rubber mill as described inexample 1. A curing system consisting of [.5 parts of diethyl amine andL5 parts of a polyfunctional aromatic compound in samples A through Eand 3 parts of phenylene diamine in sample F is milled into each stock.

After completion of the compounding, the Mooney Scorch properties ofeach sample at 250 F. are determined immediately after milling and afterstorage in a refrigerator at 2.5 C. for 1 week. Results are given intable 1X.

Sample C D E F Parts by weight:

Diethyl amine 1. 5 1. 5 1. 5 ii. 5 p-Phenylene diamine 1. HydroquinoneHexamethylene diamine.. liperazine Hexarnethylene dithiol.

p-Phenylene diamine 3.0 Mooney scorch, 121 0.,

immediately after milling:

Mo (initial reading) 22 22 148 27. 5 23 21. 3 T (minutes to 5 pointrise). 29. 5 47. 5 4. 25 5. 5 5.0 T (minutes to 10 point rise) 39 58. 25. 0 6. 5 6. 0 Mooney scorch, 121 0., alter 1 week storage at 2.5 0.:

My (initial reading) 25. 5 25. 5 200 200 96 24 '1 (minutes to 5 pointrise). 0.5 45. 5 1. 5 Tu) (minutes to 10 point rise) 39. 6 45 1. 8

1 Outside the invention.

1 No rise in 70 minutes. 1 No rise in 45 minutes.

The Mooney Scorch tests were carried out according to ASTM Dl646. Allsamples but F, which did not cure, had good physical properties after apress cure for 30 minutes at 190 C. and after post cure in an air ovenat 204 C. for 4 hours and heating an additional 24 hours at 204 C.

it is apparent from the table that samples C, D and E are very scorchy.Sample C is nearly cured before its Mooney viscosity is measured and theMooney viscosity of D and E rise very rapidly after the curing agent isadded. Samples A and B cure at a moderately rapid rate. Sample F doesnot cure at all.

The data also show that samples C, D and E cannot be stored for as longas a week even at low temperatures as they are nearly completely curedafter a week's storage at 2.5 C'. Samples A and B are very stable duringthe same low temperature storage period.

The data above show that (l) fluoroelastomer cured with the prior ansecondary monoamine-aliphatic diamine systems are very scorchy, i.e.,they prematurely vulcanize to the point that they cannot be shaped ormolded in a reasonable time after the curing agent is added, (2)aromatic polyfunctional compounds alone do not cure fluoroelastomers ata reasonable temperature and after a reasonable time, and (3) themonoamine-aromatic polyfunctional compound curing agents of thisinvention cure fluoroelastomers at a suitable rate, al lowing time forshaping during vulcanization, to yield high quality vulcanizates.

What is claimed is:

1. in the process of vulcanizing a fluoroelastomer which is a copolymerof vinylidene fluoride and at least one other ethylenically unsaturatedfluorinated monomer containing from two to six carbon atoms with anamine curing agent at a temperature of about 200 C., the improvementconsisting essentially of using as the curing agent a combination of (l)a diaikyl, dicycloalkyl, or alkylene secondary monoamine of not morethan about 24 carbon atoms in an amount providing about 0.02-0.4 part ofamino nitrogen per lOO parts of said fluoroelastomer, and (2) about0.5-2 percent by weight of said fluoroelastomer of a polyfunctionalaromatic compound having no more than 3 aromatic rings and having atleast 2 hydroxyl or primary amino groups directly attached to anaromatic nucleus.

2. A process of claim 1 wherein said monoamine (l) is diethyl amine,didodecyl amine, dicyclohexyl amine, or piperidine, and the aromaticcompound (2) is hydroquinone, metaor para-phenylene diamine,2,6-diaminotoluene, 2,4- di(p-aminobenzyl)aniline, p-aminophenol, 1,2,4-triaminobenzene or methylene dianiline.

3. A process of claim 1 wherein the amount of secondary monoamine (1)provides about 0.l-0.2 part of nitrogen per 100 parts offluoroelastomer, and the amount of aromatic compound (2) is about0.75-1.5 percent by weight of said fluoroelastomer.

4. A process of claim 3 wherein said secondary monoamine l is diethylamine and said compound (2) is para-phenylene diamine, methylenedianiline or hydroquinone.

S. A process of claim 1 wherein the aromatic compound is hydroquinone.

6. A process of claim 4 wherein the aromatic compound is hydroquinone.

7. A process of claim 4 wherein the fluoroelastomer is a copolymer ofvinylidene fluoride and hexafluoropropene; vinylidene fluoride,hexafluoropropene and tetrafluoroethylene, or vinylidene fluoride andl,2,3,3,3-pentafluoropropene.

8. A process of claim 4 wherein the fluoroelastomer is a copolymer ofvinylidene fluoride and hexafluoropropene.

9. A process of claim 1 wherein the secondary monoamine is diethylamine, dibutyl amine, didodecyl amine, piperidine or dicyclohexyl amineand the fluoroelastomer is a copolymer of vinylidene fluoride and (a)hexafluoropropene, (b) tetrafluoroethylene, (c)l,2,3,3,3-pentafluoropropene, (d) 1,1,3,3,3-pentafluoropropene, (e)chlorotrifluoroethylene, (f) perfluoroacrylic acid, (g)perfluoroacrylonitrile or (h) the acid fluoride of perfluoroacrylicacid.

10. A process of claim 19 wherein the aromatic compound is hydroquinone,methylene dianiline or para-phenylene diamine.

11. A process of claim 10 wherein the fluoroelastomer is a copolymer ofvinylidene fluoride and hexafluoropropene.

2. A process of claim 1 wherein said monoamine (1) is diethyl amine,didodecyl amine, dicyclohexyl amine, or piperidine, and the aromaticcompound (2) is hydroquinone, meta- or para-phenylene diamine,2,6-diaminotoluene, 2,4-di(p-aminobenzyl)aniline, p-aminophenol,1,2,4-triaminobenzene or methylene dianiline.
 3. A process of claim 1wherein the amount of secondary monoamine (1) provides about 0.1- 0.2part of nitrogen per 100 parts of fluoroelastomer, and the amount ofaromatic compound (2) is about 0.75- 1.5 percent by weight of saidfluoroelastomer.
 4. A process of claim 3 wherein said secondarymonoamine (1) is diethyl amine and said compound (2) is para-phenylenediamine, methylene dianiline or hydroquinone.
 5. A process of claim 1wherein the aromatic compound is hydroquinone.
 6. A process of claim 4wherein the aromatic compound is hydroquinone.
 7. A process of claim 4wherein the fluoroelastomer is a copolymer of vinylidene fluoride andhexafluoropropene; vinylidene fluoride, hexafluoropropene andtetrafluoroethylene; or vinylidene fluoride and1,2,3,3,3-pentafluoropropene.
 8. A process of claim 4 wherein thefluoroelastomer is a copolymer of vinylidene fluoride andhexafluoropropene.
 9. A process of claim 1 wherein the secondarymonoamine is diethyl amine, dibutyl amine, didodecyl amine, piperidineor dicyclohexyl amine and the fluoroelastomer is a copolymer ofvinylidene fluoride and (a) hexafluoropropene, (b) tetrafluoroethylene,(c) 1,2,3,3,3-pentafluoropropene, (d) 1,1,3, 3,3-pentafluoropropene, (e)chlorotrifluoroethylene, (f) perfluoroacrylic acid, (g)perfluoroacrylonitrile or (h) the acid fluoride of perfluoroacrylicacid.
 10. A process of claim 9 wherein the aromatic compound ishydroquinone, methylene dianiline or para-phenylene diamine.
 11. Aprocess of claim 10 wherein the fluoroelastomer is a copolymer ofvinylidene fluoride and hexafluoropropene.